1. Field of the Invention
This invention relates to a method for continuously producing a rigid plastic foam insulation board having on at least one major surface thereof a cellulosic facing member which has been impregnated with polyisocyanate.
2. Description of the Art
The usefulness of foamed plastics is well known. The rigid types, because of their especially good thermal insulation properties, find extensive application in the manufacture of laminated articles for the building industry.
These laminated articles can be made continuously or discontinuously, for example, batchwise in a mold. In either case, the, process usually involves deposition of a foam-forming mixture onto a facing sheet and bringing a second such sheet into contact with the mixture before formation of the finished article.
Particularly suitable facing sheets for such laminates from the standpoint of their inexpensiveness and ease of handling are cellulosic materials. The production of paper-faced rigid foams is described in many patents, e.g., U.S. Pat. Nos. 3,686,047, 3,903,346, 3,940,517, 4,121,958, 4,292,363, 4,366,204, and 4,764,420.
Recent U.S. Pat. Nos. 5,008,359 and 5,140,086 describe the production of polyisocyanate-impregnated cellulosic materials, and U.S. Pat. No. 5,204,176 discloses the use of such materials to form relatively rigid and strong hydrophobic sheets as siding layers for structural siding products. The sheets are said to provide weather protection, impact resistance and wind penetration resistance to a structure, and to contribute to its racking strength. Structural siding products made with the sheets can substitute for the conventional let-in braces, plywood or oriented strandboard corner sheeting used to furnish racking strength in building structures, thus saving time, labor and expense in construction.
It would be a considerable advance in the art to provide a method for the continuous production of a rigid foam insulation board which is faced with cellulosic material having a full range of facer properties desired in the art, including strength akin to that of U.S. Pat. No. 5,204,176's siding layers but without their rigidity.